Up-regulation of sphingosine-1-phosphate receptors and sphingosine kinase 1 in the peri-ischemic area after transient middle cerebral artery occlusion in mice

Neuroprotective mechanisms of A-971432: Targeting S1PR5 to modulate PI3K/Akt and MAPK pathways in cerebral ischemia/reperfusion injury

The regulation of sphingosine 1-phosphate receptor 5 (S1PR5) expression has been implicated in the pathogenesis of several neurological disorders. However, the role of the S1PR5 agonist A-971432 in cerebral ischemia/reperfusion (CI/R) injury remains unclear. In this study, we observed that the expression of S1PR5 elevated after middle cerebral artery occlusion (MCAO) in a mouse model. We administered S1PR5 intraperitoneally at a dose of 0.1 mg/kg for three consecutive days after MCAO to investigate the potential effects of A-971432. Our in vivo experiments revealed that A-971432 significantly mitigated neurological deficits and infarct volume, ameliorated neuronal injury in the ischemic cortex and hippocampus, and suppressed apoptosis and inflammatory responses. Mechanistically, A-971432 activated the PI3K/Akt/mTOR signaling pathway and inhibited the P38/ERK/JNK pathway, suggesting that both the PI3K/Akt and MAPK pathways are involved in the anti-inflammatory and anti-apoptotic effects of A-971432 in CI/R injury. Additionally, we constructed AAV-shRNA-S1pr5 viruses and found that silencing S1pr5 significantly exacerbated neuronal apoptosis and inflammatory responses in CI/R mice, exacerbating neurological deficits and expanding infarct volume. Based on these findings, we conclude that A-971432 mitigates CI/R injury-induced apoptosis and inflammatory responses through the PI3K/Akt and MAPK pathways, and S1PR5 can serve as a promising therapeutic target for ischemic stroke treatment.

Dual action of sphingosine 1-phosphate pathway in in vitro models of global cerebral ischemia

It is well accepted that sphingolipids play an important role in the pathological process of cerebral ischemia. In the present study we have investigated the involvement of sphingosine 1-phosphate (S1P) pathway in two different in vitro models of global ischemia. In organotypic hippocampal slices exposed to oxygen and glucose deprivation (OGD) we evaluated the mRNA expression of S1P metabolic enzymes and receptors (S1P1-5) by Real Time-PCR. In the same model we investigated the effect of the inhibitor of S1P lyase (SPL), LX2931, the selective antagonists of S1P2, JTE-013, and S1P3, CAY10444, quantifying the cell death in the CA1 region by propidium iodide fluorescence, and morphological and tissue organization alterations by immunohistochemistry and confocal microscopy. Moreover, we performed extracellular recordings of field excitatory postsynaptic potentials in acute slices exposed to OGD. In organotypic slices OGD induced a significant increase of SPL at mRNA level and of S1P2 and S1P3 at both mRNA and protein level. The incubation with LX2931, JTE-013 or CAY10444 was able to reduce CA1 damage induced by OGD in organotypic slices and provoked a significant delay of the onset of anoxic depolarization on acute slices. Moreover, S1P2 and S1P3 antagonists prevented the increase of TREM2 induced by OGD. Our results reveal a dual role of S1P pathway in brain ischemia: intracellular S1P, degraded via SPL, appears to be beneficial whereas signaling via S1P2 and S1P3 is detrimental to the disease. These findings support the notion that SPL, S1P2 and S1P3 are promising therapeutic targets in brain ischemia.

The sphingosine-1-phosphate signaling pathway (sphingosine-1-phosphate and its receptor, sphingosine kinase) and epilepsy

Epilepsy is one of the common chronic neurological diseases, affecting more than 70 million people worldwide. The brains of people with epilepsy exhibit a pathological and persistent propensity for recurrent seizures. Epilepsy often coexists with cardiovascular disease, cognitive dysfunction, depression, etc., which seriously affects the patient's quality of life. Although our understanding of epilepsy has advanced, the pathophysiological mechanisms leading to epileptogenesis, drug resistance, and associated comorbidities remain largely unknown. The use of newer antiepileptic drugs has increased, but this has not improved overall outcomes. We need to deeply study the pathogenesis of epilepsy and find drugs that can not only prevent the epileptogenesis and interfere with the process of epileptogenesis but also treat epilepsy comorbidities. Sphingosine-1-phosphate (S1P) is an important lipid molecule. It not only forms the basis of cell membranes but is also an important bioactive mediator. It can not only act as a second messenger in cells to activate downstream signaling pathways but can also exert biological effects by being secreted outside cells and binding to S1P receptors on the cell membrane. Fingolimod (FTY720) is the first S1P receptor modulator developed and approved for the treatment of multiple sclerosis. More and more studies have proven that the S1P signaling pathway is closely related to epilepsy, drug-resistant epilepsy, epilepsy comorbidities, or other epilepsy-causing diseases. However, there is much controversy over the role of certain natural molecules in the pathway and receptor modulators (such as FTY720) in epilepsy. Here, we summarize and analyze the role of the S1P signaling pathway in epilepsy, provide a basis for finding potential therapeutic targets and/or epileptogenic biomarkers, analyze the reasons for these controversies, and put forward our opinions. PLAIN LANGUAGE SUMMARY: This article combines the latest research literature at home and abroad to review the sphingosine 1-phosphate signaling pathway and epileptogenesis, drug-resistant epilepsy, epilepsy comorbidities, other diseases that can cause epilepsy, as well as the sphingosine-1-phosphate signaling pathway regulators and epilepsy, with the expectation of providing a certain theoretical basis for finding potential epilepsy treatment targets and/or epileptogenic biomarkers in the sphingosine-1-phosphate signaling pathway.

Sphk1/S1P pathway promotes blood-brain barrier breakdown after intracerebral hemorrhage through inducing Nlrp3-mediated endothelial cell pyroptosis

Intracerebral hemorrhage (ICH) is a severe stroke subtype with high mortality and limited therapeutic options. The blood-brain barrier (BBB) breakdown post-ICH exacerbates secondary brain injury, highlighting the need for targeted therapies to preserve the BBB integrity. We aim to investigate the role of the Sphk1/S1P pathway in BBB breakdown following ICH and to evaluate the therapeutic potential of Sphk1 inhibition in mitigating this breakdown. Using a combination of human patient samples, mouse models of ICH, and in vitro cellular assays, we assessed the expression levels of Sphk1/S1P after ICH and changes of the BBB after ICH. The Sphk1 inhibitor PF543 and siRNAs were utilized to explore the pathway's impact on BBB integrity and the underlying mechanisms. The results indicate significant upregulation of Sphk1/S1P in the peri-hematomal brain tissue after ICH, which correlates with increased BBB leakage. Pharmacological inhibition of Sphk1 with PF543 attenuates BBB leakage, reduces hematoma volume, and improves neurological outcomes in mice. At the molecular and ultrastructural level, Sphk1 inhibition protects the BBB integrity by preserving tight junction proteins and suppressing endothelial transcytosis. Furthermore, mechanistic studies reveal that Sphk1 promotes Nlrp3-mediated pyroptosis of brain endothelial cells through the ERK1/2 signaling pathway. Taken together, the Sphk1/S1P pathway plays a critical role in ICH-induced BBB breakdown, and its inhibition represents a promising therapeutic strategy for ICH management.

Chronic Low-Dose-Rate Radiation-Induced Persistent DNA Damage and miRNA/mRNA Expression Changes in Mouse Hippocampus and Blood

Our previous study demonstrated that the acute high-dose-rate (3.3 Gy/min) γ-ray irradiation (γ-irradiation) of postnatal day-3 (P3) mice with 5 Gy induced depression and drastic neuropathological changes in the dentate gyrus of the hippocampus of adult mice. The present study investigated the effects of chronic low-dose-rate (1.2 mGy/h) γ-irradiation from P3 to P180 with a cumulative dose of 5 Gy on animal behaviour, hippocampal cellular change, and miRNA and mRNA expression in the hippocampus and blood in female mice. The radiation exposure did not significantly affect the animal's body weight, and neuropsychiatric changes such as anxiety and depression were examined by neurobehavioural tests, including open field, light-dark box, elevated plus maze, tail suspension, and forced swim tests. Immunohistochemical staining did not detect any obvious loss of mature and immature neurons (NeuN and DCX) or any inflammatory glial response (IBA1, GFAP, and PDGFRα). Nevertheless, γH2AX foci in the stratum granulosum of the dentate gyrus were significantly increased, suggesting the chronic low-dose-rate irradiation induced persistent DNA damage foci in mice. miRNA sequencing and qRT-PCR indicated an increased expression of miR-448-3p and miR-361-5p but decreased expression of miR-193a-3p in the mouse hippocampus. Meanwhile, mRNA sequencing and qRT-PCR showed the changed expression of some genes, including Fli1, Hs3st5, and Eif4ebp2. Database searching by miRDB and TargetScan predicted that Fli1 and Hs3st5 are the targets of miR-448-3p, and Eif4ebp2 is the target of miR-361-5p. miRNA/mRNA sequencing and qRT-PCR results in blood showed the increased expression of miR-6967-3p and the decreased expression of its target S1pr5. The interactions of these miRNAs and mRNAs may be related to the chronic low-dose-rate radiation-induced persistent DNA damage.

A2 reactive astrocyte-derived exosomes alleviate cerebral ischemia-reperfusion injury by delivering miR-628

Ischemia and hypoxia activate astrocytes into reactive types A1 and A2, which play roles in damage and protection, respectively. However, the function and mechanism of A1 and A2 astrocyte exosomes are unknown. After astrocyte exosomes were injected into the lateral ventricle, infarct volume, damage to the blood-brain barrier (BBB), apoptosis and the expression of microglia-related proteins were measured. The dual luciferase reporter assay was used to detect the target genes of miR-628, and overexpressing A2-Exos overexpressed and knocked down miR-628 were constructed. qRT-PCR, western blotting and immunofluorescence staining were subsequently performed. A2-Exos obviously reduced the infarct volume, damage to the BBB and apoptosis and promoted M2 microglial polarization. RT-PCR showed that miR-628 was highly expressed in A2-Exos. Dual luciferase reporter assays revealed that NLRP3, S1PR3 and IRF5 are target genes of miR-628. After miR-628 was overexpressed or knocked down, the protective effects of A2-Exos increased or decreased, respectively. A2-Exos reduced pyroptosis and BBB damage and promoted M2 microglial polarization through the inhibition of NLRP3, S1PR3 and IRF5 via the delivery of miR-628. This study explored the mechanism of action of A2-Exos and provided new therapeutic targets and concepts for treating cerebral ischemia.

Edaravone Confers Neuroprotective, Anti-inflammatory, and Antioxidant Effects on the Fetal Brain of a Placental-ischemia Mouse Model

Reduced uterine perfusion pressure (RUPP) is a well-established model which mimics many clinical features of preeclampsia (PE). Edaravone is a free radical scavenger with neuroprotective, antioxidant and anti-inflammatory effects against different models of cerebral ischemia. Therefore, we aimed to elucidate the different potential mechanisms through which PE affects fetal brain development using our previously established RUPP-placental ischemia mouse model. In addition, we investigated the neuroprotective effect of edaravone against the RUPP-induced fetal brain development alterations. On gestation day (GD) 13, pregnant mice were divided into four groups; sham (SV), edaravone (SE), RUPP (RV), and RUPP+edaravone (RE). SV and SE groups underwent sham surgeries, however, RV and RE groups were subjected to RUPP surgery via bilateral uterine ligation. Edaravone (3mg/kg) was injected via tail i.v. injection from GD 14-18. The fetal brains from different groups were collected on GD 18 and subjected to further investigations. The results showed that RUPP altered the structure of fetal brain cortex, induced neurodegeneration, increased the expression of the investigated pro-inflammatory markers; TNF-α, IL-6, IL-1β, and MMP-9. RUPP resulted in microglial and astrocyte activation in the fetal brains, in addition to upregulation of Hif-1α and iNOS. Edaravone conferred a neuroprotective effect via alleviating the inflammatory response, restoring the neuronal structure and decreasing oxidative stress in the developing fetal brain. In conclusion, RUPP-placental ischemia mouse model could be a useful tool to further understand the underlying mechanisms of PE-induced child neuronal alterations. Edaravone could be a potential adjuvant therapy during PE to protect the developing fetal brain. The current study investigated the effects of a placenta-induced ischemia mouse model using reduced uterine perfusion pressure (RUPP) surgery on the fetal brain development and the potential neuroprotective effects of the drug edaravone. The study found that the RUPP model caused neurodegeneration and a pro-inflammatory response in the developing fetal brain, as well as hypoxia and oxidative stress. However, maternal injection of edaravone showed a strong ability to protect against these detrimental effects and target multiple pathways associated with neuronal damage. The current study suggests that the RUPP model could be useful for further study of the impact of preeclampsia on fetal brain development and that edaravone may have potential as a therapy for protecting against this damage.

The S1PR2-CCL2-BDNF-TrkB pathway mediates neuroinflammation and motor incoordination in hyperammonaemia

AIMS

Chronic hyperammonaemia and inflammation synergistically induce neurological impairment, including motor incoordination, in hepatic encephalopathy. Hyperammonaemic rats show neuroinflammation in the cerebellum which enhances GABAergic neurotransmission leading to motor incoordination. We aimed to identify underlying mechanisms. The aims were (1) to assess if S1PR2 is involved in microglial and astrocytic activation in the cerebellum of hyperammonaemic rats; (2) to identify pathways by which enhanced S1PR2 activation induces neuroinflammation and alters neurotransmission; (3) to assess if blocking S1PR2 reduces neuroinflammation and restores motor coordination in hyperammonaemic rats.

METHODS

We performed ex vivo studies in cerebellar slices from control or hyperammonaemic rats to identify pathways by which neuroinflammation enhances GABAergic neurotransmission in hyperammonaemia. Neuroinflammation and neurotransmission were assessed by immunochemistry/immunofluorescence and western blot. S1PR2 was blocked by intracerebral treatment with JTE-013 using osmotic mini-pumps. Motor coordination was assessed by beam walking.

RESULTS

Chronic hyperammonaemia enhances S1PR2 activation in the cerebellum by increasing its membrane expression. This increases CCL2, especially in Purkinje neurons. CCL2 activates CCR2 in microglia, leading to microglial activation, increased P2X4 membrane expression and BDNF in microglia. BDNF enhances TrkB activation in neurons, increasing KCC2 membrane expression. This enhances GABAergic neurotransmission, leading to motor incoordination in hyperammonaemic rats. Blocking S1PR2 in hyperammonaemic rats by intracerebral administration of JTE-013 normalises the S1PR2-CCL2-CCR2-BDNF-TrkB-KCC2 pathway, reduces glial activation and restores motor coordination in hyperammonaemic rats.

CONCLUSIONS

Enhanced S1PR2-CCL2-BDNF-TrkB pathway activation mediates neuroinflammation and incoordination in hyperammonaemia. The data raise a promising therapy for patients with hepatic encephalopathy using compounds targeting this pathway.

Analysis of regulatory effect of miR-149-5p on Sphingosine-1-phosphate receptor 2 of pericytes and its neuroprotective molecular mechanism after acute cerebral ischemia reperfusion in rats

To investigate the effect of miR-149-5p on sphingosine-1-phosphate receptor 2 (S1PR2) expression level and contents of matrix metalloproteinase (MMP-9) and superoxide dismutase (SOD) in the pericytes after acute cerebral ischemia reperfusion in rats, so as to clarify the neuroprotective molecular mechanism induced by miR-149-5p and provide references for the treatment of neurological diseases, 60 male SD rats aged 7-8 weeks were selected and divided randomly into test group (establishing middle cerebral artery occlusion (MCAO) model) and control group (no modeling). Rat pericytes and peripheral cerebral infarction tissues were collected 12 h, 1 d, 3 d, 5 d, and 7 d after MCAO modeling, respectively. The pericytes were identified by immunofluorescence assay (IFA) and transfected with miR-149-5p. Fluorescence quantitative PCR (FQPCR) and Western blot were adopted to detect S1PR2 expression level. The expression of S1PR2 in MCAO model rats was detected by IFA. Immunohistochemistry (IHC) and quantitative real-time PCR (qRT-PCR) were used to detect the changes of MMP9 protein and mRNA levels of SOD1, SOD2, and SOD3 in brain tissue. The results showed that mRNA level and protein expression level of S1PR2 in the test group were higher than those in the control group three days after MCAO modeling (P < 0.05); the expression of S1PR2 increased 12 h after MCAO modeling and returned to the normal level on the 5th day, and the content of MMP9 protein in brain tissue of the test group was significantly lower than that of the control group (P < 0.05); the mRNA levels and SODs activity of SOD1, SOD2, and SOD3 in the test group were higher than those in the control group (P < 0.05). Therefore, miR-149-5p played a neuroprotective role by regulating S1PR2 to change the expression levels of SODS and MMP9.

Transcriptional Regulation of Sphingosine Kinase 1

Once thought to be primarily structural in nature, sphingolipids have become increasingly appreciated as second messengers in a wide array of signaling pathways. Sphingosine kinase 1, or SK1, is one of two sphingosine kinases that phosphorylate sphingosine into sphingosine-1-phosphate (S1P). S1P is generally pro-inflammatory, pro-angiogenic, immunomodulatory, and pro-survival; therefore, high SK1 expression and activity have been associated with certain inflammatory diseases and cancer. It is thus important to develop an understanding of the regulation of SK1 expression and activity. In this review, we explore the current literature on SK1 transcriptional regulation, illustrating a complex system of transcription factors, cytokines, and even micro-RNAs (miRNAs) on the post transcriptional level.

Sphingosine 1-Phosphate Receptors in Cerebral Ischemia

Sphingosine 1-phosphate (S1P) is an important lipid biomolecule that exerts pleiotropic cellular actions as it binds to and activates its five G-protein-coupled receptors, S1P_1-5. Through these receptors, S1P can mediate diverse biological activities in both healthy and diseased conditions. S1P is produced by S1P-producing enzymes, sphingosine kinases (SphK1 and SphK2), and is abundantly present in different organs, including the brain. The medically important roles of receptor-mediated S1P signaling are well characterized in multiple sclerosis because FTY720 (Gilenya™, Novartis), a non-selective S1P receptor modulator, is currently used as a treatment for this disease. In cerebral ischemia, its role is also notable because of FTY720's efficacy in both rodent models and human patients with cerebral ischemia. In particular, some of the S1P receptors, including S1P₁, S1P₂, and S1P₃, have been identified as pathogenic players in cerebral ischemia. Other than these receptors, S1P itself and S1P-producing enzymes have been shown to play certain roles in cerebral ischemia. This review aims to compile the current updates and overviews about the roles of S1P signaling, along with a focus on S1P receptors in cerebral ischemia, based on recent studies that used in vivo rodent models of cerebral ischemia.